Method For The Production Of Fine Metal Powder, Alloy Powder And Composite Powder

ABSTRACT

There is provided a method of producing a metal powder, alloy powder or composite powder having a mean particle diameter D50 of less than or equal to 25 μm, as determined using a particle size measuring apparatus (e.g., a MICROTRAC X 100 particle size measuring apparatus) in accordance with ASTM C 1070-01. The method includes, first providing a starting powder having a mean particle diameter D50 of greater than 25 μm. The starting powder is then subjected to a deformation step, thereby forming flake-like particles having a particle diameter to particle thickness ratio of between 10:1 and 10,000:1. The flake-like particles are then subjected to comminution grinding in the presence of a grinding aid.

The invention relates to a method for producing metal, alloy orcomposite powders with a mean particle diameter D50 of at most 25 μm, astarting powder firstly being formed into flake-like particles and thesethen being comminuted in the presence of grinding aids, and to metal,alloy or composite powders obtainable thereby.

Numerous metallurgical or chemical methods are known for producing metaland alloy powders. If fine powders are to be produced, the known methodsfrequently start with the melting of a metal or an alloy.

If the melt is divided by atomisation, the powder particles formdirectly from the produced melt droplets by solidification. A largenumber of possibilities, but also limitations to the process, arisedepending on the type of cooling (treatment with air, inert gas, water),the process engineering parameters used, for instance the nozzlegeometry, gas speed, gas temperature or the nozzle material, and thematerial parameters of the melt, such as melting and solidificationpoints, solidification behaviour, viscosity, chemical composition andreactivity with the process media (W. Schatt, K.-P. Wieters in “PowderMetallurgy—Processing and Materials”, EPMA European Powder MetallurgyAssociation, 1997, 10 to 23).

As powder production by atomisation is of particular industrial andeconomic significance, various atomisation strategies have becomeestablished. Specific methods are selected depending on the powderproperties required, such as particle size, particle size distribution,particle morphology, impurities, and properties of the melts to beatomised, such as melting point or reactivity, and the tolerable costs.Nevertheless there are often limits from economic and industrial pointsof view to attaining a specific property profile of the powder (particlesize distributions, impurity contents, “designated size” yield,morphology sintering activity, etc.) at justifiable costs (W. Schatt,K.-P. Wieters in “Powder Metallurgy—Processing and Materials”, EPMAEuropean Powder Metallurgy Association, 1997, 10 to 23).

Powder production by atosation primarily has the drawback that largequantities of energy and atomising gas have to be used, and this rendersthe procedure very expensive. In particular production of fine powderfrom high melting alloys with a melting point>1,400° C. is not veryeconomical as, on the one hand, the high melting point necessitates avery high application of energy for producing the melt and, on the otherhand, the gas consumption greatly increases as the desired particle sizedecreases. In addition, difficulties often occur if at least one alloyelement has a very high affinity to oxygen. Cost advantages may beachieved during production of particularly fine alloy powder by usingspecially developed nozzles.

In addition to particle production by atomisation, other single-stagemelt metallurgical methods are also frequently used, such as what isknown as “melt-spinning”, i.e. pouring a melt onto a cooled roll,whereby a thin, usually easily comminutable strip is produced, or whatis referred to as “crucible melt extraction”, i.e. the immersion of acooled profiled roll rotating at high speed into a molten metal, whereinparticles or fibres are obtained.

A further important variant of powder production is the chemical methodvia reduction of metal oxides or metal salts. However, it is notpossible to obtain alloy powders in this manner (W. Schatt, K.-P.Wieters in “Powder Metallurgy—Processing and Materials”, EPMA EuropeanPowder Metallurgy Association, 1997, 23 to 30).

Extremely fine particles which have particle sizes of less than onemicrometre may also be produced by the combination of evaporation andcondensation of metals and alloys and via gas phase reactions (W.Schatt, K.-P. Wieters in “Powder Metallurgy—Processing and Materials”,EPMA European Powder Metallurgy Association, 1997, 39 to 41). Thesemethods are very expensive, however.

If cooling of the melt takes place in a relatively large volume/block,mechanical method steps of coarse, fine and superfine comminution arenecessary to produce metal or alloy powder that may be processed bypowder metallurgy. An overview of mechanical powder production is givenby W. Schat, K.-P. Wieters in “Powder Metallurgy—Processing andMaterials”, EPMA European Powder Metallurgy Association, 1997, 5 to 47.

Mechanical comminution, in particular in mills, as the oldest method ofparticle size adjustment, is very advantageous from an industrialperspective as it inexpensive and may be applied to a large number ofmaterials. However, it makes certain demands on the process material,for example with respect to size of the pieces and brittleness of thematerial. In addition, comminution cannot be pursued as desired; rathera grinding equilibrium forms, which also occurs if the grinding processis begun with relatively fine powders. The conventional grindingprocesses are modified if the physical limits of the capacity forcomminution are attained for the respective grinding stock and certainphenomena, such as embrittlement at low temperatures or the effect ofgrinding aids, improve the grinding behaviour or the capacity forcomminution.

A method of fine comminution of relatively brittle pre-comminutedmaterial that is particularly suitable in many cases involves theconcept of gas contra-jet mills of which there are numerous commercialsuppliers, for example Hosokawa-Alpine or Netzsch-Condux. This method isprevalent and provides, in particular in the case of brittle materials,considerable advantages from industrial (low level of impurities,autogenic grinding) and financial perspectives compared to conventionalmills using purely mechanical comminution, such as ball mills oragitated ball mills. Jet mills attain their industrial and thus theirfinancial limits with comminution of ductile starting powders, in otherwords materials that are difficult to comminute, and low designatedparticle sizes. This is explained by the decreasing kinetic energy ofthe powder particles being comminuted in the gas jet. As the kineticenergy of the powder particles is to be applied only via the carriergas, the specific energy requirement during superfine comminutionincreases to financially unjustifiable ranges and in the case of powderswith high ductility is practically inapplicable. The sintering activityof these powders thus comminuted does not correspond to the sinteringactivity of powder particles produced by conventional grinding either.

Very fine particles may be obtained, for example, by combining grindingsteps with hydrogenation and dehydrogenation reactions, including thecombination of reaction products to form the desired phase compositionof the powder (I. R. Harris, C. Noble, T. Bailey, Journal of the LessCommon Metals, 106 (1985), L1 to L4). However, this method is limited toalloys which contain elements that may form stable hydrides. Mechanicalinfluences on the comminution in the form of lattice defects or otherdefects may thus be substantially avoided. This is particularlyimportant if the functional properties of the powder particles, forexample the crystallites, critically affect the properties of the powderproduct, such as in NdFeB permanent magnets.

Said methods always meet their limits if it is a matter of producingvery fine powders of ductile metals or alloys which have both highreactivity to oxygen and high sintering activities.

The coldstream process was developed for producing products of thistype, metallic particles subjected to intense cooling being centriged atextremely high speeds of up to 1 Mach via a venturi tube onto a cooledpanel. It is thus allegedly possible to produce a product with aparticle size between 5 and 10 μm (W. Schatt, K.-P. Wieters in “PowderMetallurgy—Processing and Materials”, EPMA European Powder MetallurgyAssociation, 1997, 9 to 10). The act of accelerating the starting powderto the speed of sound necessitates an extremely high application ofenergy in this method. Furthermore, abrasion problems may occur and,owing to the interaction between particles and counterplate, criticalimpurities are introduced into the grinding stock.

A further method for producing fine powder from ductile material ismechanical alloying. In this process agglomerates are obtained byintensive grinding treatment, which agglomerates are made up ofcrystallites that are approximately 10 to 0.01 μm in size. The metallicductile material changes as a result of the high mechanical stress insuch a way that fine individual particles may possibly form. Thesecontain the composition typical of the alloy. However, the drawback ofthis process is that considerable impurities are sometimes introduced,primarily by abrasion. Usually, however, it is precisely theuncontrolled abrasion that is an obstacle to industrial use. In additionthere is the fact that discrete superfine particles are only producedafter a very long grinding period. Fine metal and alloy powderstherefore cannot be economically produced by mere mechanical alloying.

The object of the present invention therefore consists in providing aprocess for producing fine, in particular ductile, metal, alloy orcomposite powders, the method being particularly suitable for producingalloys, i.e. multi-component systems, and allowing fundamentalproperties, such as particle size, particle size distribution, sinteringactivity, impurity content or particle morphology to be purposefullyadjusted or influenced.

The object is achieved according to the invention by a two-stage method,a starting powder firstly being formed into flake-like particles andthese then being comminuted in the presence of grinding aids.

The invention therefore relates to a method for producing metal, alloyor composite powders with a mean particle diameter D50 of at most 25 μm,determined using the particle measuring apparatus Microtrac® X 100 toASTM C 1070-01, from a starting powder with a greater mean particlediameter, wherein

-   a) the particles of the starting powder are processed in a shaping    step into flake-like particles, of which the particle diameter to    particle thickness ratio is between 10:1 and 10,000:1, and-   b) the flake-like particles are subjected to comminution grinding in    the presence of a grinding aid.

The particle measuring apparatus Microtrac® X 100 is commerciallyavailable from Honeywell, U.S.A.

For determining the particle diameter to particle thickness ratio theparticle diameter and the particle thickness are determined using alight-optical microscope. For this purpose, the flake-like powderparticles are firstly mixed with a viscous, transparent epoxy resin in aratio of 2 volume fractions resin and 1 volume fraction flakes. The airbubbles introduced during mixing are then expelled by evacuation of thismixture. The then bubble-free mixture is poured over a planar substrateand then rolled out using a roller. The flake-like particles are thusoriented in the flow field between roller and substrate. The preferredposition manifests itself in that the surface normals of the flakes areoriented on average parallel to the surface normals of the planarsubstrate, in other words the flakes are arranged in layers on averageflat on the substrate. After curing, suitable samples of suitabledimensions are worked from the epoxy resin plate on the substrate. Thesamples are microscopically examined perpendicularly and parallel to thesubstrate. By using a microscope with a calibrated lens and by takinginto account the adequate particle orientation at least 50 particles aremeasured and an average is formed from the measured values. This averagerepresents the particle diameter of the flake-like particles. Followinga perpendicular cut through the substrate and the sample to be examined,the particle thicknesses are determined using the microscope with acalibrated lens, which microscope was also used to determine theparticle diameter. Care should be taken that only particles locatedoptimally parallel to the substrate are measured. As the particles arecompletely surrounded by the transparent resin, selecting suitablyoriented particles and reliably assigning the limitations of theparticles to be evaluated do not present any difficulties. Again atleast 50 particles are measured and an average formed from the measuredvalues. This average represents the particle thickness of the flake-likeparticles. The particle diameter to particle thickness ratio iscalculated from the previously ascertained values.

In particular fine, ductile metal, alloy or composite powders may beproduced with the method according to the invention. Ductile metal,alloy or composite powders are in his case taken to mean those powderswhich, in the event of mechanical stress until the yield point isreached, undergo plastic expansion or deformation before significantmaterial damage (material embrittlement, material rupture) occurs.Plastic material changes of this type are dependent on the material andare in the range of 0.1 per cent up to several 100 per cent, based onthe starting length.

The degree of ductility, i.e. the capacity of materials to plastically,i.e. permanently, deform under the effect of mechanical stress may bedetermined or described by mechanical tensile or pressure testing.

For determining the degree of ductility by tensile testing what isreferred to as a tensile sample is produced from the material to beassessed. This may be, for example, a cylindrical sample which, halfwayalong its length, has a reduction in diameter of approximately 30 to 50%over a length of approximately 30 to 50% of the total sample length. Thetensile sample is fixed in a fixing device of an electromechanical orelectrohydraulic tensile testing machine. Length sensors are installedon average of the sample over a measuring length which is approximately10% of the overall sample length, before actual mechanical testing.These sensors allow the increase in the length to be followed in theselected measuring length during application of a mechanical tensilestress. The stress is increased until the sample fractures and theplastic content of the change in length is evaluated using thestress-strain recording. Materials which achieve a plastic change inlength of at least 0.1% in an arrangement of this type will be calledductile in the context of this specification.

Analogously it is also possible to subject a cylindrical materialsample, which has a diameter to thickness ratio of approximately 3:1, tomechanical compressive stress in a commercially available pressuretesting machine. Permanent deformation of the cylindrical sample occursin this case as well after application of an adequate mechanicalcompressive stress. Once the pressure has been relieved and the sampleremoved, an increase in the diameter to thickness ratio of the sample isdetermined. Materials which achieve a plastic change of at least 0.1% ina test of this type are also called ductile in the context of thisspecification.

Fine ductile alloy powders which have a degree of ductility of at least5% are preferably produced by the method according to the invention.

According to the invention the capacity for comminution of alloy ormetal powders that cannot be comminuted further per se is improved bythe use of mechanically, mechanochemically and/or chemically actinggrinding aids which are purposefully added or produced in the grindingprocess. A fundamental aspect of this approach is that the chemical“desired composition” of the powder thus produced cannot be changedoverall or influenced even such that the processing properties, such asthe sintering behaviour or flowability, are improved.

The method according to the invention is suitable for producing a widevariety of fine metal, alloy or composite powders with a mean particlediameter D50 of at most 25 μm.

For example metal, alloy or composite powders of a compositioncorresponding to formula IhA-iB-jC-kD  (I)may be obtained, wherein

-   A represents one or more of the elements Fe, Co, Ni,-   B represents one or more of the elements V, Nb, Ta, Cr, Mo, W, Mn,    Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt,-   C represents one or more of the elements Mg, Al, Sn, Cu, Zn, and-   D represents one or more of the elements Zr, Hf, rare-earth metal,    and h, i, j and k indicate the percentages by weight, wherein-   h, i, j and k in each case independently of one another represent 0    to 100% by weight,    with the proviso that the sum of h, i, j and k is 100% by weight.

In formula I preferably

-   A represents one or more of the elements Fe, Co, Ni,-   B represents one or more of the elements V, Cr, Mo, W, Ti,-   C represents one or more of the elements Mg, Al and-   D represents one or more of the elements Zr, Hf, Y, La

h preferably represents 50 to 80% by weight, in particular preferably 60to 80% by weight. i preferably represents 15 to 40% by weight, inparticular preferably 18 to 40% by weight. j preferably represents 0 to15% by weight, in particular preferably 5 to 10% by weight. k preferablyrepresents 0 to 5% by weight, in particular preferably 0 to 2% byweight.

The metal, alloy or composite powders produced according to theinvention are distinguished by a small mean particle diameter D50. Themean particle diameter D50 is preferably at most 15 μm, determined toASTM C 1070-01 (measuring apparatus: Microtrac® X 100).

By way of example powders which already have the composition of thedesired metal, alloy or composite powder may be used as the startingpowder. In the method according to the invention however, it is alsopossible to use a mixture of several starting powders which only producethe desired composition after suitable selection of the mixing ratio.The composition of the produced metal, alloy or composite powder mayalso be influenced by the choice of grinding aid, if this remains in theproduct.

Powders with spherical or irregularly shaped particles and a meanparticle diameter D50, determined to ASTM C 1070-01 of greater than 25μm, preferably 30 to 2,000 μm, in particular preferably 30 to 1,000 μm,are preferably used as the starting powders.

The required starting powders may be obtained, for example, byatomisation of molten metals and, if necessary, subsequent screening orsifting.

According to the invention the starting powder is firstly subjected to adeformation step. The deformation step may be carried out in knowndevices, for example in a rolling mill, an eddy mill, a high-energy millor an attritor or an agitated ball mill. By suitably selecting theprocess engineering parameters, in particular as a result of the effectof mechanical stresses which are sufficient to achieve plasticdeformation of the material or the powder particles, the individualparticles are deformed, so they ultimately have a flake-like form, thethickness of the flakes preferably being 1 to 20 μm. This may takeplace, for example, by one-off stressing in a roller or a hammer mill,by repeated stressing in “small” deformation steps, for example bypercussive grinding in an eddy mill or a Simoloyer®, or by a combinationof percussive and frictional grinding, for example in an attritor or aball mill. The high material stress during this deformation may lead tostructural damage and/or material embrittlement which may be used in thefollowing steps for comminuting the material.

Known molten metallurgical fast solidification processes may also beused for producing strips or “flakes”. These, like the mechanicallyproduced flakes, are then suitable for comminution grinding describedbelow.

The device in which the deformation step is carried out, the grindingmedia and the other grinding conditions are preferably selected suchthat the impurities as a result of abrasion and/or reactions with oxygenor nitrogen are as small as possible and below the critical value forthe application of the product or are within the specification relevantto the material.

This is possible for example by suitable selection of the grindingcontainer and grinding media materials and/or the use of gases hinderingoxidation and nitriding and/or the addition of protecting solventsduring the deformation step.

In a particular embodiment of the method according to the invention theflake-like particles are produced in a fast solidification step, forexample by what is known as “melt spinning”, directly from the melt bycooling on or between one or more, preferably cooled roller(s), soflakes are directly formed.

According to the invention the flake-like particles obtained in thedeformation step are subjected to comminution grinding. In the process,on the one hand, the particle diameter to particle thicknessratiochanges, primary particles with a particle diameter to particlethickness ratio of 1:1 to 10:1 usually being obtained and, on the otherhand, the desired mean particle diameter of at most 25 μm is adjustedwithout particle agglomerates that are difficult to comminute occurringagain.

Comminution grinding may take place for example in a mill, for instancean eccentric mill, but also in Gutbett rolls, extruders or similardevices which bring about material shattering owing to differentmovement and stress rates in the flake.

According to the invention comminution grinding is carried in thepresence of a grinding aid. Liquid grinding aids, waxes and/or brittlepowder for example, may be used as the grinding aid. In this case thegrinding aids may act mechanically, chemically or mechanochemically.

By way of example the grinding aid may be paraffin oil, paraffin wax,metal powder, alloy powder, metal sulphides, metal salts, salts oforganic acids and/or hard material powder.

Brittle powder or phases act as mechanical grinding aids and may beused, for example, in the form of alloy, element, hard material,carbide, silicide, oxide, boride, nitride or salt powder. By way ofexample pre-comminuted element and/or alloy powders are used which,together with the starting powder used, which is difficult to comminute,produce the desired composition of the product powder.

Brittle powders used are preferably those which comprise binary, ternaryand/or higher compositions of the elements A, B, C and/or D that occurin the starting alloy used, A, B, C and D having the meanings givenabove.

Liquid and/or easily deformable grinding aids, for example waxes, mayalso be used. Other examples include hydrocarbons, such as hexane,alcohols, amines or aqueous media. These are preferably compounds whichmay be required for the following steps of further processing and/orwhich may be easily removed after comminution grinding.

It is also possible to use specific organic compounds which are knownfrom pigment production where they are used to stabilisenon-agglomerating individual flakes in a liquid environment.

In a particular embodiment grinding aids are used which enter a targetedchemical reaction with the starting powder to achieve the grindingprogress and/or for adjusting a specific chemical composition. These maybe, for example, decomposable chemical compounds, of which only one ormore constituents are required for adjusting a desired composition, itbeing possible to substantially remove at least one component orconstituent by a thermal process.

Reducible and/or decomposable compounds, such as hydrides, oxides,sulphides, salts and sugars are mentioned as examples which are at leastpartially removed from the grinding stock in a subsequent processingstep and/or powder metallurgical processing of the product powder, theremaining residue chemically complementing the powder composition in thedesired manner.

It is also possible that the grinding aid is not added separately but isproduced in situ during comminution grinding. In this case the proceduremay, for example, be such that the grinding aid is produced by adding areactive gas which reacts under the conditions of comminution grindingwith the starting powder while forming a brittle phase. Hydrogen ispreferably used as the reactive gas.

The brittle phases which are produced during treatment with the reactivegas, for example by formation of hydrides and/or oxides, may usually beremoved again by appropriate method steps after comminution grinding orduring processing of the fine metal, alloy or composite powder obtained.

If grinding aids are used which are not removed, or are only partiallyremoved, from the metal, alloy or composite powder produced according tothe invention, they are preferably selected such that the remainingconstituents affect a property of the material in a desired manner, suchas improving the mechanical properties, reducing the corrodibility,increasing the hardness and improving the abrasion behaviour or thefrictional and sliding properties. The use of a hard material ismentioned here by way of example, which is increased in content in asubsequent step to the extent that the hard material may be furtherprocessed with the alloy component to form a hard metal or a hardmaterial alloy composite.

After the deformation step and comminution grinding the primaryparticles of the metal, alloy or composite powder produced have,according to the invention, a mean particle diameter D50, determined toASTM C 1070-01 (Microtrac® X 100), of at most 25 μm.

In addition to the formation of fine primary particles, the knowninteractions between superfine particles can lead to the formation ofrelatively coarse secondary particles (agglomerates), of which theparticle diameter is far greater than the desired mean particle diameterof at most 25 μm, despite the use of grinding aids.

A deagglomeration step therefore preferably follows comminutiongrinding, during which the agglomerates are broken open and the primaryparticles liberated. Deagglomeration may, for example, take place byapplying shear forces in the form of mechanical and/or thermal stressesand/or by removing separation layers previously introduced in theprocess between primary particles. The deagglomeration methods to beapplied in particular are oriented toward the degree of agglomeration,the intended used and the susceptibility to oxidation of the superfinepowder and the admissible impurities in the finished product.

Deagglomeration may, for example, take place by mechanical methods, forinstance by treatment in a gas contrajet mill, screening, sieving ortreatment in an attritor, a kneader or a rotor-stator dispergator. Theuse of a stress field, as generated in ultrasound treatment, thermaltreatment, for example dissolution or conversion of a previouslyintroduced separating layer between the primary particles by cryo- orhigh-temperature treatments, or a chemical conversion of introduced orpurposefully produced phases, is also possible.

Deagglomeration is preferably carried out in the presence of one or moreliquids, dispersing aids and/or binders. A slurry, a paste, a kneadingcompound or a suspension with a solids content between 1 and 95% byweight may thus be obtained. Solids contents between 30 and 95% byweight may be directly processed by known powder technological processessuch as injection moulding, film casting, coating, and hot-moulding, andare then reacted in suitable steps of drying, releasing and sintering toform an end product.

A gas contrajet mill, which is operated under inert gases, such as argonor nitrogen, is preferably used for deagglomeration of particularlyoxygen-sensitive powders.

The metal, alloy or composite powders produced according to theinvention are distinguished from conventional powders with identicalmean particle diameters and identical chemical composition which areproduced, for example, by atomisation, by a range of particularproperties.

The invention therefore also relates to metal, alloy or compositepowders with a mean particle diameter D50 of at most 25 μm, determinedusing the particle measuring apparatus Microtrac® X 100 to ASTM C1070-01, which are obtainable by the method according to the invention.

The metal, alloy and composite powders according to the inventionexhibit, for example, excellent sintering behaviour. At low sinteringtemperatures the same sintering densities may be attained as in powdersproduced by atomisation. Starting from powder compacts of a definedcompressed density, higher sintering densities may be achieved at thesame sintering temperature. This increased sintering activity is alsoexhibited, for example, in the fact that, until the maximum contractionis attained, the contraction during the sintering process is greaterthan in conventionally produced powders.

The invention therefore also relates to metal, alloy or compositepowders with a mean particle diameter D50 of at most 25 μm, determinedusing the particle measuring device Microtrac® X 100 to ASTM C 1070-01,wherein, until the maximum contraction is attained, the contraction,determined using a dilatometer to DIN 51045-1 has at least 1.05 timesthe contraction of a metal, alloy or composite powder with identicalchemical composition and identical mean particle diameter D50, thepowder to be investigated being compressed to a compressed density of50% of the theoretical density before the contraction is measured.

The powder to be investigated may be compressed by adding conventionalcompression-assisting agents, such as paraffin wax or other waxes orsalt or organic acids, for example zinc stearate,

Metal alloy or composite powders which are produced by atomisation andby comparison with which the powders according to the invention haveimproved sintering behaviour, are to be taken to mean those powderswhich are produced by conventional atomisation known to the personskilled in the art.

The advantageous sintering behaviour of the metal, alloy or compositepowders according to the invention may also be recognised in the courseof sintering and contraction curves, as shown, for example, in FIG. 7.

FIG. 7 shows, for a comparison powder (V) and a powder (PZD) accordingto the invention, the course of the contraction S or the contractionrate AS in each case in relative units as a function of the temperatureT_(N) standardised to the respective sintering temperature T_(S).

The comparison powder (V) is a product produced by atomisation underinert conditions and with a composition corresponding to that of thematerial described in Example 1 and the morphology of this powder. Theparticle size distribution (D50 approximately 8.4 μm) corresponds tothat as shown in FIG. 5. The powder (PZD) according to the invention isa powder produced according to Example 1 with the morphology illustratedin FIG. 6 and an oxygen content of 0.4% by weight.

After mixing with 3% by weight microwax as the compression-facilitatingadditive powder compacts were produced from the two powders in acompression mould by applying a single-axle pressure of 400 to 600 mPa.The green density was in both cases approx. 40% of the theoreticaldensity. These compacts were accordingly sintered individually in adilatometer to DIN 51045-1 under protective gas conditions and usingargon as the process gas. Heating at a rate of approx. 1 K/min(corresponding to approx. 6 * 10⁻⁴ *T_(S)/min where T_(S): approx. 1,600K) took place in the process. The push rod of the dilatometer does notexert any pressure on the sample which supplies a measurable quantityfor sintering contraction in the temperature range that is of interestfor sintering (approx. 0.5 T_(S) to approx. 0.95 T_(S)).

The organic pressing aid is expelled to a temperature of approximately0.45 * T_(S). The actual sintering process takes place thereafter byfurther heating at the same heating rate from approx. 0.5 T_(S) toapprox. 0.99 T_(S).

The advantages of the PZD powder lead to the following observations andto general rules which are illustrated with the aid of FIG. 7. For thispurpose, the required terms, which allow a general description of thesintering processes, shall firstly be introduced:

-   ^(V)T₉₀ and ^(PZD)T₉₀: temperatures (in standardised units according    to T_(N)=T/T_(S)) at which the two sintering bodies, at a heating    rate of approx 6 * 10⁻⁴ * T_(S), have attained a contraction of 90%,    based on the same final contraction (=100) attained.-   ^(V)T₁₀ and ^(PZD) ₁₀: temperatures (in standardised units according    to T_(N)=T/T_(S)) at which the two sintering bodies, at a heating    rate of approx 6 * 10⁻⁴ * T_(S), have attained a contraction of 10%,    based on the same final contraction (=100) attained,-   ^(V)T₁ and ^(PZD)T₁: temperatures (in standardised units according    to T_(N)=T/T_(S)) at which the two sintering bodies, at a heating    rate of approx 6 * 10⁻⁴ * T_(S), have attained a contraction of 1%,    based on the same final contraction (=100) attained. Contraction    starts at these temperatures.-   ^(V)T_(max) and ^(PZD)T_(max): temperatures (in standardised units    T_(N)=T/T_(S)) at which the maximum contraction rate is reached.-   ^(V)S(T_(N)), ^(PZD)S(T_(N)): contraction as a function of the    standardised temperature T_(N).-   ^(V)AS(T_(N)), ^(PZD)AS(T_(N)): temperature-dependent contraction    rate d(S(T_(N)))/dT_(N), determined from the contraction curves to    be compared ^(V)S(T_(N)) and ^(PZD)S(T_(N)).-   ^(V)S_(max) and ^(PZD)S_(max): maximum value of contraction rates,    determined from the contraction curves derived according to    temperature ^(V)S(T_(N)) and ^(PZD)S(T_(N)).

The following general product properties of the powders according to theinvention are obtained compared to conventionally produced atomisedpowders: (^(PZD)T_(max) − ^(PZD)T₁₀)/^(PZD)T_(max) > (^(V)T_(max) −^(V)T₁₀)/^(V)T_(max) (I) ^(PZD)T_(max) < ^(V)T_(max) (II) ^(PZD)T₁₀ <^(V)T₁₀ (III) ^(PZD)T₁ < ^(V)T₁ (IV) ^(PZD)S_(max) < ^(V)S_(max) (V)(^(PZD)T_(max) − ^(PZD)T₁₀) > (^(V)T_(max) − ^(V)T₁₀) (VI)(^(PZD)T_(max) − ^(PZD)T₁) > (^(V)T_(max) − ^(V)T₁) (VII) (^(PZD)T₉₀ −^(PZD)T₁₀) > (^(V)T₉₀ − ^(V)T₁₀) (VIII) (^(PZD)T₉₀ − ^(PZD)T₁) >(^(V)T₉₀ − ^(V)T₁) (IX)

The following conclusions with respect to the different behaviour ofpowder (PZD powder) produced according to the invention and comparisonpowders produced by conventional atomisation may be drawn from theseinequities:

-   The sintering range for PZD powder is wider.-   The temperature at which contraction begins, at which, based on    identical final contraction, 10% of this final contraction is    attained and at which contraction attains its maximum, is lower in    PZD powders.-   The peaks of the contraction rates obtained from the standardised    illustration of FIG. 7 mean that PZD powders have a lower    contraction rate at ^(PZD)T_(max) than the comparison powder at    ^(V)T_(max).-   The initial temperature range up to the contraction peak is wider    for PZD powders.-   The temperature range from the start of contraction up to the    maximum contraction is greater for PZD powders.-   The temperature range between the temperature at which contraction    of 10% was attained up to the temperature at which contraction of    90% was attained is greater for PZD powders.-   The temperature range from the start of contraction up to the    temperature at which 90% of the final contraction is attained is    greater for PZD powders.

These statements relate to single-phase starting states of the powders.In the event that there are further phases not all of the inequalities(I) to (IX) have to always be met together, in particular very highcontraction rates may occur locally on PZD powder compacts as a resultof particular sintering activations of liquid phases, which ratesconstitute a further advantage with respect to processing capacity.However, the validity of the inequalities (III), (IV), (VIII) and (IX)is unaffected in this case as well.

The metal, alloy and composite powders according to the invention aredistinguished, owing to a particular particle morphology with roughparticle surface, moreover by outstanding compression behaviour and,owing to a comparatively broad particle size distribution, by highcompressed density. This manifests itself in that compacts made ofatomised powder have a lower bending strength, under otherwise identicalproduction conditions, than the compacts made of powders according tothe invention and with the same chemical composition and mean particlesize D50. A further improvement in the compression behaviour may beachieved if powder mixtures comprising 1 to 95% by weight metal, alloyor composite powders according to the invention and 99 to 5% by weightatomised powder are used.

The sintering behaviour of powders produced according to the inventionmay also be purposefully influenced by the choice of grinding aid. Thusone or more alloys which, owing to their low melting point compared tothe starting alloy form liquid phases during heating which improve theparticle rearrangement and the material diffusion and thus the sinteringbehaviour and the contraction behaviour and thus allow higher sinteringdensities to be attained at the same sintering temperature or at lowersintering temperatures the same sintering density as may be achievedwith the comparison powders, may be used as the grinding aid. Chemicallydecomposable compounds, of which the decomposition products with thebasic material produce liquid phases or phases with increased diffusioncoefficients which facilitate compression, may also be used.

X-ray analyses of the metal, alloy or composite powders according to theinvention show a propagation of X-ray reflexes compared with X-rayreflexes that are obtained for powders with the same mean particlediameter and the same chemical composition which were obtained byatomisation. The propagation is demonstrated by the propagation of halfwidths. Usually the half widths of the X-ray reflexes are propagated bya factor >1.05. This is caused by the mechanical stressed stated of theparticles, the existence of a higher dislocation density, i.e.disturbances to the solid in the atomic range, and the crystallite sizein the particles. In the case of composite powders, alloy- and/orprocess-induced phases occur in the diffractograms in addition to thepropagations of the X-ray reflexes of the main phase, which phases aresignificant for the contraction properties.

The method according to the invention allows production of metal, alloyand composite powders, in which oxygen, nitrogen, carbon, boron andsilicon contents are purposefully adjusted. Oxide and/or nitride phasesmay form in the case of introduction of oxygen or nitrogen as a resultof the high application of energy. Phases of this type may be desirablefor specific applications as they may lead to strengthening of material.This effect is known as the “particle dispersion strengthening” effect(PDS effect). However, the introduction of such phases is oftenassociated with a deterioration in the processing properties (forexample compressibility, sintering activity). Owing to the generallyinert properties of the dispersoids with respect to the alloycomponents, the latter may therefore have a sintering-inhibiting effect.

As a result of the comminution grinding to be carried out according tothe invention, said phases are immediately superfinely distributed inthe produced powder. The phases formed (for example oxides, nitrides,carbides, borides) are therefore much more finely and homogeneouslydistributed in the metal, alloy and composite powders according to theinvention than in conventionally produced powders. This again leads toincreased sintering activity compared with discretely introduced phasesof the same kind.

The processing properties of the metal, alloy and composite powdersaccording to the invention, for example the compression and sinteringbehaviour, and the capacity for processing by metal powder injectionmoulding (MIM), slurry-based methods or tape casting, may often beimproved even further by adding metal, alloy or composite powdersconventionally produced, in particular by atomisation.

The invention therefore also relates to mixtures containing 1 to 95% byweight of a metal, alloy or composite powder and 99 to 5% by weight of aconventionally produced metal, alloy or composite powder.

The mixtures according to the invention preferably contain 10 to 70% byweight of a metal, alloy or composite powder according to the inventionand 90 to 30% by weight of a conventionally produced metal, alloy orcomposite powder.

The conventionally produced metal, alloy or composite powder accordingto the invention is preferably a powder which has been produced byatomisation.

The conventionally produced metal, alloy or composite powder may havethe same chemical composition as the PZD powder contained in themixture. Mixtures of this type are distinguished from pure PZD powdersin particular by a further improvement in compression behaviour.

However, it is also possible that PZD powder and conventionally producedpowder have a different chemical composition in the mixture. In thiscase the composition may be purposefully changed and as a resultspecific powder properties and consequently the material properties maybe purposefully adjusted.

The following examples serve to describe the invention in more detail,wherein the examples are intended to facilitate understanding of theprinciple according to the invention and are not to be understood as alimitation thereof.

EXAMPLES

The mean particle diameters D50 given in the examples were determinedusing a Microtrac® X 100 from Honeywell, U.S.A. to ASTM C 1070-01.

Example 1

A Nimonic® 90 type alloy melt atomised by means of argon and with thecomposition Ni20Cr16Co2.5Ti1.5Al was used as the starting powder. Thealloy powder obtained was screened between 53 and 25 μm. The density wasapprox. 8.2 g/cm³. The staring powder had substantially sphericalparticles, as may clearly be seen in FIG. 1 (scanning electronmicroscope image (SEM image) magnified 300 times).

The starting powder was subjected to deformation grinding in a verticalagitated ball mill (Netzsch Feinmahltechik; PR 1S type), so theoriginally spherical particles assumed flake-like forms. The followingparameters were used in particular:

-   -   Grinding container volume: 51    -   Speed of rotation: 400 rpm    -   Circumferential speed: 2.5 m/s    -   Ball filling: 80 vol. % (bulk volume of the balls)    -   Grinding container material: 100Cr6 (DIN 1.3505: approx. 1.5% by        weight Cr, approx. 1% by weight C, approx. 0.3% by weight Si,        approx. 0.4% by weight Mn, <0.3% by weight Ni, <0.3% by weight        Cu, remainder Fe)    -   Ball material: hard metal (WC-10Co)    -   Ball diameter: approx. 6 mm (total mass: 25 kg)    -   Originally weighed in quantity of powder: 500 g    -   Duration of treatment: 2 h    -   Solvent: ethanol (approx. 21).

FIG. 2 is a SEM image magnified 300 times of the flakes produced in thedeformation step. The high degree of material deformation, which wascaused by the specific grinding treatment, compared with the startingpowder may be seen. Damage to the structure of the material (crackformation) may also clearly be seen.

Comminution grinding was then carried out. “hat is referred to as aneccentric vibration grinding mill (Siebtechnik GmbH, ESM 324) with thefollowing process engineering parameters was used:

-   -   Grinding container volume: 51 operated as a satellite (diameter        20 cm, length approx. 15 cm)    -   Ball filling: 80 vol. % (bulk volume of the balls)    -   Grinding container material: 100 Cr6 (DIN 1.3505: approx. 1.5%        by weight Cr, approx. 1% by weight C, approx. 0.3% by weight Si,        approx. 0.4% by weight Mn, <0.3% by weight Ni, <0.3% by weight        Cu, remainder Fe)    -   Ball material: 100 Cr6    -   Ball diameter: 10 mm    -   Originally weighed in quantity of powder: 150 g    -   Grinding aid 2 g paraffin    -   Oscillation amplitude: 12 mm    -   Grinding atmosphere: argon (99.998%).

After a grinding duration of 2 hours superfine particle agglomerateswere obtained.

FIG. 3 is a SEM image magnified 1,000 times of the product obtained. Thecauliflower-like structure of the agglomerate (secondary particle) maybe seen, the primary particles having particle diameters of much lessthan 25 μm.

A sample of the primary particles or superfine particle agglomerates wassubjected in a third method step to deagglomeration by ultrasoundtreatment in isopropanol in an ultrasonic device TG 400 (SonicUltraschallanlagenbau GmbH) lasting 10 minutes at 50% maximum power toobtain separated primary particles.

The particle size distribution of the deagglomerated sample wasdetermined using a Microtrac® X 100 (manufacturer: Honeywell, U.S.A.) toASTM C 1070-01. FIG. 4 shows the particle size distribution thusobtained. The D50 value of the starting powder was 40 μm and was reducedto approx 15 μm by the treatment according to the invention.

The remaining quantity of primary particles from comminution grindingwere subjected in an alternative third method step to deagglomeration bytreatment in a gas contrajet mill and subsequent ultrasound treatment inisopropanol in an ultrasonic device TG 400 (Sonic UltaschallanagenbauGmbH) at 50% of the maximum power. The particle size was againdetermined using a Microtrac® X 100. FIG. 5 shows the particle sizedistribution obtained. The D50 value was then only 8.4 μm. This provesthe possibility of further increasing the fine fraction in the powderproduced according to the invention by high-energy post-treatment.

FIG. 6 shows a SEM image (×600 magnification) of the powder aftertreatment in the gas contrajet mill. By using suitable screening methodsit is accordingly possible to obtain alloy powders with even narrowerparticle size distribution. D50 values of less than approx. 8 μm maythus be industrially and economically achieved.

The introduced grinding aid paraffin may be removed during powdermetallurgical further processing of the alloy powder by thermaldecomposition and/or evaporation and may be used as a compression aid.

Example 2 Production of Fe24Cr10Al1Y Superfine Powders Using MechanicalGrinding Aids without Changing the Composition of the Starting Powder

500 g of a spherical starting powder of a Fe24Cr10Al1Y alloy with a meanparticle diameter D50 of 40 μm was processed to form flakes in adeformation stage under conditions analogous to those described inExample 1.

Comminution grinding was then carried out in an eccentric vibrationgrinding mill, as described in Example 1. A mixture of comminutedbrittle Fe70Cr, Fe60Al and Fe16Y powders with a mean particle diameterof approx. 40 μm and fine Fe powder with a mean particle diameter D50 of10 μm was added as the grinding aid.

15 g grinding aid was used for comminution grinding. The addition ofapprox. 10 vol. % of a mechanically acting grinding aid is a typicalcontent for this step. Smaller quantities of grinding aids may also beuseful as a function of the proposed aim. The composition of thegrinding aid used is summarised in Table 1. A mixture containing 65% byweight Fe, 24% by weight Cr, 10% by weight Al and 1% by weight Y wasobtained. The chemical composition of the starting powder is accordinglynot altered by the choice of given alloy contents. A specificdistribution of the components used (starting powder, grinding aid) ispresent in the composite powder obtained as a result of productionaccording to the invention, so the composite powder undergoes ametallurgical change during further processing, for example by sinteringor another thermal process. TABLE 1 Composition of a mechanical grindingaid Component Quantity [g] Fe [g] Cr [g] Al [g] Y [g] Fe16Y 0.93 0.78 00 0.15 Fe60Al 2.50 1.0 0 1.5 0 Fe70Cr 5.14 1.54 3.6 0 0 Fe 6.43 6.43 0 00 Total 15 9.75 3.6 1.5 0.15

A composite powder with a mean particle diameter D50 of 15 μm wasobtained after comminution grinding and deagglomeration in an ultrasonicfield. It was possible to obtain an alloy in the metallurgical sensefrom a composite powder of this type by thermal post-treatment.

Example 3 Production of Fe24Cr10Al1Y Superfine Powders Using MechanicalGrinding Aids and Changing the Composition Compared with the StartingPowder

In contrast to Example 2, a change in the chemical composition wasdesired or allowed during the grinding operation. An atonised alloy ofcomposition Fe25,6Cr10,67Al with a mean particle diameter D50 of 40 μmwas subjected to a deformation step under the conditions described inExample 1. Flake-like particles with a mean particle diameter D50 of 70μm were obtained, of which the appearance did not significantly differfrom that in Example 1.

Comminution grinding was then carried out. The procedure corresponded tothat in Example 1 but 10 g of a Fe16Y powder with a mean particlediameter D50 of 40 μm were used as the grinding aid and the grindinglasted 2 hours.

Table 2 gives the composition and quantity of flake-like starting alloyand the grinding aid added for comminution grinding. TABLE 2 Compositionof the flake-like starting alloy and mechanical grinding aid usedComponent Quantity [g] Fe [g] Cr [g] Al [g] Y [g] Fe25,6Cr10,67Al 15095.6 38.4 16.0 0 Fe16Y 10 8.4 0 0 1.6 Total 160 104 38.4 16.0 1.6

As may be seen from Table 2, the composite powder obtained had thecomposition Fe24Cr10Al1Y. The composite powder was subjected to anultrasound treatment after which a composite powder with a mean particlediameter D50 of 13 μm was obtained.

Example 4

The procedure was as in Example 3, a mixture of a plurality of brittlematerials and pure iron powder being used as the grinding aid.

Table 3 contains the composition and original weighed in quantities ofthe starting powder and grinding aid. The brittle grinding aids Fe60Al,Fe70Cr and Y2, 2H were brought to a mean particle diameter D50 of 40 μmbefore use in a separate grinding step. The Fe powder used had a meanparticle diameter D50 of 10 μm. TABLE 3 Composition of the flake-likestarting alloy and the mechanical grinding aid used Component Quantity[g] Fe [g] Cr [g] Al [g] Y [g] Fe25,6Cr10,67Al 150.00 95.60 38.40 16.000.00 Fe60Al 1.19 0.48 0.00 0.71 0.00 Fe70Cr 2.35 0.71 1.64 0.00 0.00Y2,2H 1.66 0.00 0.00 0.00 1.66 Fe 10.00 10.00 0.00 0.00 0.00 Total165.20 106.79 40.04 16.71 1.66

As may be seen from Table 3, the composite powder obtained had thecomposition Fe24Cr10Al1Y. The composite powder was subjected to anultrasound treatment after which a composite powder with a mean particlediameter D50 of 15 μm was obtained.

Example 5 Production of a Fe24Cr10Al1Y Superfine Powder from Two FeCrAlMaster Alloys and Fe16Y as the Single Brittle Mechanical Grinding Aid

Flakes with mean particle diameters D50 of 70 μm, of which theappearance did not significantly differ from the powder produced in FIG.2, were produced in separate deformation steps analogously to Example 1from two atomised alloys with the composition Fe19,9Cr24,8Al andFe27,9Cr5Al with mean particle diameters D50 of 40 μm.

The particularly brittle Fe16Y alloy was used as the only grinding aidduring subsequent comminution grinding, which alloy had previously beencomminuted to a mean particle diameter D50 of approx. 40 μm. Theprocedure was as in Example 1, grinding lasting 2.5 hours.

Table 4 contains the composition and original weighed in quantities ofthe two flake-like FeCrAl starting alloys and of the brittle grindingaid (Fe16Y). TABLE 4 Composition of the flake-like starting alloys andthe mechanical grinding aid used Component Quantity [g] Fe [g] Cr [g] Al[g] Y [g] Fe19,9Cr24,8Al 43 23.8 8.6 10.5 0 Fe27,9Cr5Al 107 71.8 29.85.5 0 Fe16Y 10 8.4 0 0 1.6 Total 160 104 38.4 16 1.6

As may be seen from Table 3, the composite powder obtained had thecomposition Fe24Cr10Al1Y. The composite powder was subjected to anultrasound treatment after which a composite powder with a mean particlediameter D50 of 12 μm was obtained.

Example 6 In situ Production of the Grinding Aid

An atomised Ni15Co10Cr5,5Al4,8Ti3Mo1V alloy, which is commerciallyavailable under the model name IN 100®, was subjected, as described inExample 1, to a deformation step under an inert atmosphere.

No brittle grinding aid was added during subsequent comminutiongrinding, rather it was formed in situ during the grinding process. Forthis purpose, the eccentric vibration grinding mill was flooded with agas mixture consisting of 94 vol. % argon and 6 vol. % hydrogen. Thegrinding container was thermally insulated, so a processing temperatureof approx. 300° C. was established during the grinding process owing tothe application of energy. The remaining grinding conditionscorresponded to the procedure described in Example 1. The elevatedtemperature and the hydrogen content of the process gas lead to theformation of brittle Ti—H and V—H compounds which acted in the samemanner as the grinding aids introduced in Examples 1 to 5 and thus ledto comminution. After grinding that lasted 3 h under ahydrogen-containing atmosphere, an alloy powder with a mean particlediameter D50 of 13 μm was achieved.

The chemical composition of the resultant superfine powder differed onlyslightly from that of the starting powder. The hydrogen content rose to<1,000 ppm. During further processing of the alloy powder producedaccording to the invention the hydrogen content fell to below approx. 50ppm again as a result of sintering under vacuum.

Example 7 Si Powder as the Mechanical Grinding Aid

Spherical atomised Ni38Cr8,7Al1,09Hf with a mean particle diameter D50of 40 μm was subjected, as described in Example 1, to a deformationstep.

150 g of the flake-like powder produced in the attritor were subjected,as described in Example 1, to comminution grinding in an eccentricvibration grinding mill, 13 g Si powder with a mean particle diameterD50 of 40 μm being added as the grinding aid. After grinding that lasted2 h an alloy powder with a mean particle diameter D50 of 10.5 μm and thedesired composition Ni35Cr8Al8Si1Hf was obtained. The silicon used isdesirable or necessary in terms of alloy engineering. Of the possiblebrittle grinding aids Si is particularly suitable owing to itsproperties. After treatment the oxygen content was approx. 0.4% byweight.

Example 8

Spherical atomised Ni38Cr8,7Al1,09Hf with a mean particle diameter D50of 40 μm was subjected, as described in Example 7 by using an attritor(agitated ball mill), to a deformation step.

Subsequent comminution grinding was carried out in the presence of Sipowder (13 g) as the grinding aid, likewise in an agitated ball mill,the following technical parameters being adjusted:

-   -   Grinding container volume: 51    -   Ball filling: 80 vol. %    -   Grinding container material: 100 Cr6    -   Ball material: 100 Cr6    -   Ball diameter: 3.5 mm    -   Originally weighed in quantity of powder: 150 g        Ni38Cr8,7Al1,09Hf    -   Circumferential speed: 4.2 m/s    -   Grinding liquid: ethanol    -   Grinding duration: 1.5 h    -   Grinding aid 13 g Si powder (D50: approx. 40 μm)

After grinding that lasted 1.5 hours and subsequent ultrasonicdeagglomeration an alloy powder with a mean particle diameter D50 of 13μm, measured by Microtrac® X 100, was obtained. The silicon used in thiscase was desirable or necessary in terms of alloy engineering in orderto adjust the end composition Ni38Cr8,7Al1,09Hf and in terms of processengineering for attaining the desired grinding effect. Of the elementstat may be considered silicon is best suited as the grinding aid owingto its brittleness. This grinding process led to an increase in theoxygen content in the powder. At the conclusion of the grinding processthe oxygen content was 0.4% by weight.

Example 9

A spherical atomised Ni17Mo15Cr6Fe5W1Co alloy with a mean particlediameter D50 of 40 μm, which is commercially available under the nameHastelloy®, was subjected, as described in Example 1, to a deformationstep.

The flake-like particles obtained were comminution ground in aneccentric vibration grinding mill in the presence of tungsten carbide asthe grinding aid and under the following conditions:

-   -   Grinding container volume: 51    -   Ball filling: 80 vol. %    -   Grinding container material: 100 Cr6    -   Ball material: WC-10Co hard metal material    -   Ball diameter: 6.3 mm    -   Originally weighed in quantity of powder: 150 g    -   Oscillation amplitude: 12 mm    -   Grinding atmosphere: argon (99.998%)    -   Grinding duration: 90 minutes    -   Grinding aid 13.5 g WC powder D50=1.8 μm)

The result of comminution grinding was an alloy hard material compositepowder in which the alloy components had been comminuted to a meanparticle diameter D50 of approx. 5 μm and the hard material component toa mean particle diameter D50 of approx. 1 μm. The hard materialparticles were substantially homogenously distributed in the alloypowder volume.

The alloy hard material composite powder could be processed byconventional process steps to form a spray powder, For this purpose, 797g WC with a mean particle diameter D50 to ASTM B 330 (FSSS) of 1 μm,ethanol, PVA (polyvinyl alcohol) and suspension stabilisers were addedto 163 g of the alloy hard material composite powder produced accordingto the invention for dispersing and generating a suspension. Asuspension was produced which consisted to 25 vol. % of the metallicbinding phase and to 75 vol. % of the WC hard material phase. Thissuspension was further processed by spray granulation and classificationto form a green spray powder with a particle size of 20 to 63 μm. Theorganic auxiliaries were firstly removed from this green spray powder bygas evolution at 100 to 400° C. and sintering then took place at approx.1,300° C. under an inert atmosphere. In the process solid bonds wereproduced in the spray granules and less solid bonds between theindividual granule grains. Deagglomeration and classification into thedesired grain fraction (for example 15 to 45 μm) finally took place. Thepowder thus obtained could be further processed by thermal injection ina known manner to form hard metal or components coated with analloy-hard material composite.

Example 10

Titanium powder with a mean particle diameter D50 of 100 μm wasprocessed according to the invention and analogously to Example 1 toform flakes.

The flakes were then further processed in a comminution step analogouslyto Example 1, 10 g TiH₂ being added as the grinding agent to the Tiflakes used (original weighed in quantity: 150 g). After comminutiongrinding there was a fine titanium powder with a mean particle diameterD50 of approx. 15 μm.

The titanium powder produced according to the invention could be furtherprocessed by conventional process steps to form mould parts. To protectagainst oxidation the titanium powder produced according to theinvention was stored in an organic solvent, for example n-hexane. Longchain hydrocarbons, such as paraffin or amines, were added prior topowder metallurgical further processing. For this purpose, the paraffinwas dissolved for example in n-hexane, added to the powder and then-hexane was then evaporated with continuous circulating of the powder.A superficial seal against uncontrolled absorption of oxygen wasobtained thereby and the improvement in compressibility achieved. Thisprocedure allows the titanium powder to be processed in air.

After processing in terms of powder technology to form mould parts bysingle-axle compression, removal of the organic constituents in athermal treatment, thermal decomposition of the grinding aid andsintering to form substantially dense mould parts took place,

Example 11

Flakes made of an alloy 17-4 PH® (Fe17Cr12Ni4Cu2.5Mo0.3Nb) and which hadbeen produced analogously to Example 1, were treated in a contrajetmill. The flakes had a particle diameter to particle thickness ratio ofapprox. 1,000:1 and a mean particle diameter D50 of 150 μm. Thecontrajet mill was operated with inert gas. Atomised spherical material,which had not been pre-treated, of the same alloy with a particlediameter between 100 and 63 μm was used as the grinding aid. Thegrinding chamber (volume: approx. 51) was filled with 2.51 powder bulkvolume (67% by weight grinding aid and 33% by weight flakes) and thegrinding process initiated. The fine fraction produced was separated at10 μm by corresponding adjustments of a sifter connected downstream ofthe mill.

In contrast to the earlier examples, comminution grinding and thegenerally required deagglomeration were performed in one step by theprocedure described. A particular feature of this procedure is the useof characteristic or alloy-like powder that cannot, or may barely, becomminuted and which leads to an increased application of energy in thegrinding process and thus to an improved grinding effect.

Example 12

An atomised Ni17Mo15Cr6Fe5W1Co alloy with a mean particle diameter of100 to 63 μm, which is commercially available under the name Hastelloy®,was mechanically treated in a high energy mill (eccentric vibrationmill) under the following conditions:

-   -   Grinding container volume: 51 (diameter 20 cm, length approx. 15        cm)    -   Ball filling: 80 vol. %    -   Grinding container material: 100 Cr6    -   Ball material: WC-Co hard metal    -   Ball diameter: 10 mm    -   Originally weighed in quantity of powder: 300 g    -   Oscillation amplitude: 12 mm    -   Grinding atmosphere: argon (99.998%)    -   Grinding duration: 2 h

Flakes were produced which had a diameter to thickness ratio of 1:2 anda flake thickness of approx. 20 μm.

Comminution grinding then took place in a gas contrajet mill. Duringcomminution particles which had a particle diameter of <20 μm wereremoved by suitably adjusting a sifter connected downstream. A finealloy powder which, after ultrasound treatment, had a mean particlediameter D50 of 12 μm and a D90 value of 20 μm, determined using aMicrotrac® X 100, was thus produced.

1. A method of producing a powder product comprising: (a) providing astarting powder having a mean particle diameter D50 of greater than 25μm; (b) subjecting said starting powder to a deformation step, therebyforming flake-like particles having a particle diameter to particlethickness ratio of between 10:1 and 10,000:1; and (c) subjecting theflake-like particles of step (b) to comminution grinding in the presenceof a grinding aid, wherein said powder product is selected from thegroup consisting of metal powder, alloy powder and composite powder, andsaid powder product has a mean particle diameter D50 of at most 25 μm asdetermined using a particle size measuring apparatus in accordance withASTM C 1070-01.
 2. The method of claim 1 further comprising adeagglomeration step, said deagglomeration step following comminutiongrinding step (c).
 3. The method of claim 1 wherein said powder producthas a composition represented by the following formula I,hA-iB-jC-kD  (I)wherein, A represents at least one element selected fromthe group consisting of Fe, Co, and Ni, B represents at least oneelement selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn,Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir, and Pt, C represents atleast one element selected from the group consisting of Mg, Al, Sn, Cu,and Zn, and D represents at least one element selected from the groupconsisting of Zr, Hf, and rare-earth metals, and h, i, j and k eachindependently represent percentages by weight of 0 to 100% by weight,with the proviso that the sum of h, i, j and k is 100% by weight.
 4. Themethod of claim 3 wherein, B represents at least one element selectedfrom the group consisting of V, Cr, Mo, W, and Ti, C represents at leastone element selected from the group consisting of Mg, and Al, and Drepresents at least one element selected from the group consisting ofZr, Hf, Y, and La.
 5. The method of claim 3 wherein, h represents 50 to80% by weight, i represents 15 to 40% by weight, j represents 0 to 15%by weight, and k represents 0 to 5% by weight.
 6. The method of claim 1wherein the powder product has a mean particle diameter D50 of at most15 μm.
 7. The method of claim 1 wherein the starting powder comprisesparticles having shapes selected from the group consisting of sphericalshapes and irregular shapes.
 8. The method of claim 1 whereindeformation step (b) is carried out in an apparatus selected from thegroup consisting of a rolling mill, an eddy mill, a high-energy mill andan attritor.
 9. The method of claim 1 wherein said grinding aid isselected from the group consisting of liquid grinding aids, waxes,brittle powder and combinations thereof.
 10. The method of claim 9wherein the grinding aid is selected from the group consisting ofparaffin oil, paraffin wax, metal powder, alloy powder, metal sulphide,salt, hard material powder and combinations thereof.
 11. The method ofclaim 1 wherein the grinding aid is formed in situ during comminutiongrinding step (c).
 12. The method of claim 11 wherein the grinding aidis formed in situ by adding a reactive gas which reacts, undercomminution grinding conditions, with the starting powder while forminga brittle phase.
 13. The method of claim 2 wherein the deagglomerationstep is carried out in an apparatus selected from the group consistingof a gas contrajet mill, an ultrasound bath, a kneader and arotor-stator.
 14. The method of claim 2 wherein the deagglomeration stepis carried out in the presence of at least one material selected fromthe group consisting of liquids, dispersing aids and binders.
 15. Thepowder prepared by the method of claim
 1. 16. A powder product having amean particle diameter D50 of at most 25 μm, determined using a particlemeasuring apparatus in accordance with ASTM C 1070-01, wherein, saidpowder product has a maximum contraction value, determined using adilatometer in accordance with DIN 51045-1, of at least 1.05 times thecontraction value of a comparative powder having identical chemicalcomposition and identical mean particle diameter D50 relative to saidpowder product, the powder product and the comparative powder each beingcompressed to a compressed density of 50% of theoretical density beforemeasuring contraction values, and further wherein said powder product isselected from the group consisting of metal powder, alloy powder andcomposite powder.
 17. A mixture comprising: (i) 1 to 95% by weight ofthe powder product of claim 1; and (ii) 99 to 5% by weight of anatomized powder produced by atomization, said atomized powder beingselected from the group consisting of atomized metal powder, atomizedalloy powder and atomized composite powder.
 18. The method of claim 1wherein said particle size measuring apparatus is a MICROTRAC X 100particle size measuring apparatus.
 19. The powder of claim 16 whereinsaid particle size measuring apparatus is a MICROTRAC X 100 particlesize measuring apparatus.